Terminal Cl Ligands Research Articles

Structure‐Activity Relationships of the Structural Analogs Au8Cu1 and Au8Ag1 in the Electrocatalytic CO2 Reduction Reaction

AbstractOwing to the significant attention directed toward alloy metal nanoclusters, it is crucial to explore the relationship between their structures and their performance during the electrocatalytic CO2 reduction reaction (eCO2RR) and discover potential synergistic effects for the design of novel functional nanoclusters. However, a lack of suitable analogs makes this investigation challenging. In this study, we synthesized a well‐defined pair of structural analogs, [Au8Cu1(SAdm)4(Dppm)3Cl]2+ and [Au8Ag1(SAdm)4(Dppm)3Cl]2+ (Au8Cu1 and Au8Ag1, respectively), and characterized them. Single‐crystal X‐ray diffraction analysis revealed that Au8M1 (M=Cu/Ag) consists of a tetrahedral Au3M1 core capped by three (Dppm)Au staples, one Au2(SR)3 staple, one lone SR ligand, and a terminal Cl ligand. Ag and Cu were doped at the same site in the Au8M1 nanoclusters, which has rarely been reported. Au8Cu1 exhibited a significantly higher CO Faradaic efficiency (FECO; ~82.2 %) during eCO2RR than that of Au8Ag1 (FECO; ~33.1 %). Density functional theory calculations demonstrated that *COOH is the key intermediate in the reduction of CO2 to CO. The formation of *COOH on Au8Cu1 is more thermodynamically stable than on Au8Ag1, and Au8Cu1 shows a smaller *CO formation energy than that on Au8Ag1, which promotes the reduction of CO2. We believe that the structural analogs Au8Cu1 and Au8Ag1 offer a suitable template for the in‐depth investigation of structure‐property correlations at the atomic level.

Structure-Activity Relationships of the Structural Analogs Au8Cu1 and Au8Ag1 in the Electrocatalytic CO2 Reduction Reaction.

Owing to the significant attention directed toward alloy metal nanoclusters, it is crucial to explore the relationship between their structures and their performance during the electrocatalytic CO2 reduction reaction (eCO2RR) and discover potential synergistic effects for the design of novel functional nanoclusters. However, a lack of suitable analogs makes this investigation challenging. In this study, we synthesized a well-defined pair of structural analogs, [Au8Cu1(SAdm)4(Dppm)3Cl]2+ and [Au8Ag1(SAdm)4(Dppm)3Cl]2+ (Au8Cu1 and Au8Ag1, respectively), and characterized them. Single-crystal X-ray diffraction analysis revealed that Au8M1 (M=Cu/Ag) consists of a tetrahedral Au3M1 core capped by three (Dppm)Au staples, one Au2(SR)3 staple, one lone SR ligand, and a terminal Cl ligand. Ag and Cu were doped at the same site in the Au8M1 nanoclusters, which has rarely been reported. Au8Cu1 exhibited a significantly higher CO Faradaic efficiency (FECO; ~82.2 %) during eCO2RR than that of Au8Ag1 (FECO; ~33.1 %). Density functional theory calculations demonstrated that *COOH is the key intermediate in the reduction of CO2 to CO. The formation of *COOH on Au8Cu1 is more thermodynamically stable than on Au8Ag1, and Au8Cu1 shows a smaller *CO formation energy than that on Au8Ag1, which promotes the reduction of CO2. We believe that the structural analogs Au8Cu1 and Au8Ag1 offer a suitable template for the in-depth investigation of structure-property correlations at the atomic level.

Synthesis, Spectral Characterization, Crystal Structure and Antibacterial Activity of dichloro-{2-[(4-fluorophenyl)iminomethyl]pyridine-κ2N,N'}mercury(II)

The title complex has been prepared using (4-Fluoro-phenyl)-pyridin-2-ylmethylene-amine bidentate Schiff base ligand (L) and HgCl2. The Hg(II) center in the title compound, [HgCl2(C12H9FN2)], is covalently bonded to three Cl atoms and two N atoms of the diimine ligand. Mercury ion mononuclear fragment that forms a polymeric structure due to bridging chloride ligands is in a distorted trigonal–bipyramidal coordination environment formed by the bis-chelating N-heterocyclic ligand, two bridging Cl ligands and one terminal Cl ligand. One of the bridging Hg—Cl bonds is significantly longer than the other. In the crystal, weak C—H.....Cl hydrogen bonds are observed in addition to π-π stacking interactions. It crystallizes in the Orthorhombic space group P212121 with a = 7.2248 (3) Å, b = 8.7713 (3) Å, c = 20.0217 (7) Å, α = 90.00°, β = 90.00, γ = 90.00°, V = 1268.79(8) Å3, R1 = 0.023 and wR2= 0.062 [I > 2σ(I)] respectively. The antibacterial activities of the complex, ligand and metal salt were tested against Gram-positive bacteria Staphylococcus aureus and Gram-negative bacteria Escherichia coli studied by disk diffusion method.

Crystal structure of bis-[μ-2-(diiso-propyl-phosphor-yl)propan-2-olato-κ(3) O (1),O (2):O (1)]bis-[chlorido-oxidovanadium(IV)

The dinuclear mol-ecule of the title complex, [VOCl{μ-OC(Me)2P(iPr)2-κ(2) O}]2 or [V2(C9H20O2P)2Cl2O2], which was obtained due to an unexpected oxidation reaction, is centrosymmetric, with the inversion centre located in the middle of the central V2O2 core. These core O atoms arise from the symmetry-related 2-(diiso-propyl-phosphor-yl)propan-2-olate dianions. The V(IV) atom is additionally bonded to one terminal Cl ligand, the second O atom of the dianion and double bonded to a vanadyl O atom, leading to an overall distorted square-pyramidal VO4Cl coordination polyhedron with the vanadyl O atom as the apex. An intra-molecular C-H⋯Cl contact helps to establish the mol-ecular configuration. In the crystal, mol-ecules are stacked in rows parallel to [001] and are linked by C-H⋯Cl contacts to form chains running in the same direction.

A second monoclinic polymorph of di-μ-chlorido-bis(chlorido{2-[(4-ethylphenyl)iminomethyl]pyridine-κ2N,N′}copper(II))

The title compound, [Cu2Cl4(C14H14N2)2], is a new polymorph of a previously reported compound [Dehghanpour et al. (2011 ▶). Acta Cryst. E67, m1296]. The current polymorph was obtained from an acetonitrile solution of the title compound. Like the first polymorph, it is monoclinic (space group P21/c). The unique CuII ion in the title centrosymmetric dinuclear complex is in a distorted trigonal–bipyramidal coordination environment formed by the bis-­chelating N-heterocyclic ligand, two bridging Cl ligands and one terminal Cl ligand. In the crystal, weak C—H⋯Cl hydrogen bonds are observed in addition to π–π stacking inter­actions, with a centroid–centroid distance of 3.6597 (18) Å.

Reactivity of [Re2(CO)8(MeCN)2] With 1-vinylimidazole: X-ray Structures of [Re2(CO)8{η 1-NC3H3N(CH=CH2)}2] and [ReCl2(CO)2{η 1-NC3H3N(CH=CH2)}2

Treatment of [Re2(CO)8(MeCN)2] with excess 1-vinylimidazole in refluxing benzene gives three new compounds [Re2(CO)9{η 1-NC3H3N(CH=CH2)}] (1), [Re2(CO)8{η 1-NC3H3N(CH=CH2)}2] (2) and [ReCl2(CO)2{η 1-NC3H3N(CH=CH2)}2] (3) in 11, 32 and 2% yields, respectively. The solid-state structures of complexes 2 and 3 have been determined by single crystal X-ray diffraction studies. Compound 2 crystallizes in the monoclinic space group C2/c, with lattice parameters a = 13.8378(5) A, b = 11.8909(5) A, c = 14.4591(6) A, β = 116.6470(10)°, Z = 4 and V = 2131.99(15) A3. Compound 3 crystallizes in the monoclinic space group C2/c, with lattice parameters a = 10.1028(3) A, b = 13.5640(5) A, c = 12.5398(4) A, β = 109.637(2)°, Z = 4 and V = 1618.4(9) A3. The disubstituted dinuclear compound 2 contains two 1-vinylimidazole ligands coordinated through the imino nitrogen atoms at the equatorial sites, whereas the mononuclear compound 3 contains two carbonyl ligands, two N coordinated η 1-1-vinylimidazole ligands and two terminal Cl ligands. Two dinuclear complesxes [Re2(CO)9{η 1-NC3H3N(CH=CH2)}] (1) and [Re2(CO)8{η 1-NC3H3N(CH=CH2)}2] (2) and the mononuclear [ReCl2(CO)2{η 1-NC3H3N(CH=CH2)}2] (3) were obtained from the reaction of [Re2(CO)8(MeCN)2] with excess 1-vinylimidazole at 80 °C. The X-ray structrures of 2 and 3 are described.

Reactions of rhenium and manganese carbonyl complexes with 1,8-bis(diphenylphosphino)naphthalene: Ligand chelation, C–H and C–P bond-cleavage reactions

Reaction of [Re 2(CO) 8(MeCN) 2] with 1,8-bis(diphenylphosphino)naphthalene (dppn) afforded three mono-rhenium complexes fac-[Re(CO) 3(κ 1:η 1-PPh 2C 10H 6)(PPh 2H)] ( 1), fac-[Re(CO) 3{κ 1:κ 1:η 1-(O)PPh 2C 10H 6(O)PPh(C 6H 4)}] ( 2) and fac-[ReCl(CO) 3(κ 2-PPh 2C 10H 6PPh 2)] ( 3). Compounds 1– 3 are formed by Re–Re bond cleavage and P–C and C–H bond activation of the dppn ligand. Each of these three complexes have three CO groups arranged in facial fashion. Compound 1 contains a chelating cyclometalated diphenylnaphthylphosphine ligand and a terminally coordinated PPh 2H ligand. Compound 2 consists of an orthometalated dppn-dioxide ligand coordinated in a κ 1:κ 1:η 1-fashion via both the oxygen atoms and ortho-carbon atom of one of the phenyl rings. Compound 3 consists of an unchanged chelating dppn ligand and a terminal Cl ligand. Treatment of [Mn 2(CO) 8(MeCN) 2] with a slight excess of dppn in refluxing toluene at 72 °C, gave the previously reported [Mn 2(CO) 8(μ-PPh 2) 2] ( 4), formed by cleavage of C–P bonds, and the new compound fac-[MnCl(CO) 3(κ 2-PPh 2C 10H 6PPh 2)] ( 5), which has an unaltered chelating dppn and a terminal Cl ligand. In sharp contrast, reaction of [Mn 2(CO) 8(MeCN) 2] with slight excess of dppn at room temperature yielded the dimanganese [Mn 2(CO) 9{κ 1-PPh 2(C 10H 7)}] ( 6) in which the diphenylnaphthylphosphine ligand, formed by facile cleavage of one of the P–C bonds, is axially coordinated to one Mn atom. Compound 6 was also obtained from the reaction of [Mn 2(CO) 9(MeCN)] with dppn at room temperature. The XRD structures of complexes 1– 3, 5, 6 are reported.

Dirhenium carbonyl complexes bearing 2-vinylpyridine, morpholine and 1-methylimidazole ligands

Treatment of the labile compound [Re 2(CO) 8(MeCN) 2] with 2-vinylpyridine in refluxing benzene affords exclusively the new compound [Re 2(CO) 8(μ-η 1:η 2-NC 5H 4CH CH 2)] ( 1) in 39% yield in which the μ-η 1:η 2-vinylpyridine ligand is coordinated to one Re atom through the nitrogen and to the other Re atom via the olefinic double bond. Reaction of [Re 2(CO) 8(MeCN) 2] with morpholine in refluxing benzene furnishes two compounds, [Re 2(CO) 9(η 1-NC 4H 9O)] ( 2) and [Re 2(CO) 8(η 1-NC 4H 9O) 2] ( 3) in 5% and 29% yields, respectively. Reaction of [Re 2(CO) 8(MeCN) 2] with 1-methylimidazole gives [Re 2(CO) 8{η 1-NC 3H 3N(CH 3)} 2] ( 4) and the mononuclear compound fac-[ReCl(CO) 3{η 1-NC 3H 3N(CH 3)} 2] ( 5) in 18% and 26% yields, respectively. In the disubstituted compounds 2 and 4, the heterocyclic ligands occupy equatorial coordination sites. The mononuclear compound 5 consists of three CO groups, two N coordinated η 1-1-methylimidazole ligands and a terminal Cl ligand. The XRD structures of complexes 1, 3 and 5 are reported.

Reactivity of [Re 2(CO) 8(MeCN) 2] with thiazoles: Hydrido bridged dirhenium compounds bearing thiazoles in different coordination modes

Reactions of the labile compound [Re 2(CO) 8(MeCN) 2] with thiazole and 4-methylthiazole in refluxing benzene afforded the new compounds [Re 2(CO) 7{μ-2,3-η 2-C 3H(R)NS}{η 1-NC 3H 2(4-R)S}(μ-H)] ( 1, R = H; 2, R = CH 3), [Re 2(CO) 6{μ-2,3-η 2-C 3H(R)NS}{η 1-NC 3H 2(4-R)S} 2(μ-H)] ( 3, R = H; 4, R = CH 3) and fac-[Re(CO) 3(Cl){η 1-NC 3H 2(4-R)S} 2] ( 5, R = H; 6, R = CH 3). Compounds 1 and 2 contain two rhenium atoms, one bridging thiazolide ligand, coordinated through the C(2) and N atoms and a η 1-thiazole ligand coordinated through the nitrogen atom to the same Re as the thiazolide nitrogen. Compounds 3 and 4 contain a Re 2(CO) 6 group with one bridging thiazolide ligand coordinated through the C(2) and N atoms and two N-coordinated η 1-thiazole ligands, each coordinated to one Re atom. A hydride ligand, formed by oxidative-addition of C(2)–H bond of the ligand, bridges Re–Re bond opposite the thiazolide ligand in compounds 1– 4. Compound 5 contains a single rhenium atom with three carbonyl ligands, two N-coordinated η 1-thiazole ligands and a terminal Cl ligand. Treatment of both 1 and 2 with 5 equiv. of thiazole and 4-methylthiazole in the presence of Me 3NO in refluxing benzene afforded 3 and 4, respectively. Further activation of the coordinated η 1-thiazole ligands in 1– 4 is, however, unsuccessful and results only nonspecific decomposition. The single-crystal XRD structures of 1– 5 are reported.

Redetermination of Cs[MnCl3(H2O)2

The structure of the one-dimensional anti­ferromagnet caesium diaqua­trichloro­manganate(II) was re-refined based on area-detector data, including the positions of H atoms. The MnII atom, on a twofold rotation axis, is in a distorted octa­hedral coordination by two bridging Cl ligands in trans positions, two terminal Cl ligands and two aqua ligands, both in cis positions. Hydrogen bonds of the type O—H⋯Cl connect octa­hedra along the chain and link the chains into layers which are separated by the Cs ions (also on twofold axes). The structure is discussed in comparison with non-isotypic related compounds of the morphotropic series AMCl3(H2O)2 (A = Cs, Rb, K and M = Mn, Fe, Co).

Structure and solution properties of the cadmium(II)-substituted tungstoarsenate [Cd 4Cl 2( B-α-AsW 9O 34) 2] 12−

The cadmium(II)-substituted tungstoarsenate [Cd 4Cl 2( B-α-AsW 9O 34) 2] 12− ( 1) has been synthesized and characterized in the solid state by XRD, IR, elemental analysis and in solution by 183W and 111Cd NMR. Single crystal X-ray analysis was carried out on Cs 4K 3Na 5[Cd 4Cl 2( B-α-AsW 9O 34) 2] · 20H 2O. Polyanion 1 consists of two lacunary [ B-α-AsW 9O 34] 9− Keggin moieties linked via a rhomblike (Cd 4O 14Cl 2) group leading to a sandwich-type structure. Interestingly, the two external Cd atoms have a terminal Cl ligand, but the derivative with terminal water ligands, [Cd 4(H 2O) 2( B-α-AsW 9O 34) 2] 10− ( 2), can also be prepared as shown by 183W and 111Cd solution NMR.

Synthesis, crystal structures and spectroscopic characterization of two neutral heterobimetallic clusters MS 4Cu 4(pz Me2) 6X 2 (where M = Mo ( 1) or W ( 2), X = Cl ( 1) or disordered Cl/Br ( 2), and pz Me2 = 3,5-dimethylpyrazole)

The title complexes were synthesized in acetone by the reaction of [ n-Bu 4N] 2[MoS 4Cu 4Cl 4] and pz Me2 for compound 1, and n-Bu 4NBr, [NH 4] 2[WS 4], CuCl and pz Me2 for compound 2. X-ray diffraction studies of 1 and 2 demonstrate that four of the six edges of the tetrahedral [MS 4] 2− core are bridged by four copper atoms, giving a pentanuclear structure MS 4Cu 4(pz Me2) 6X 2 (M = Mo, W) with the five metal atoms essentially coplanar. The four Cu atoms exhibit two different coordination modes. Each of one pair of mutually trans Cu atoms is coordinated by two (μ 3-S) atoms and two nitrogen atoms of pz Me2 rings, giving a distorted tetrahedral CuS 2N 2 arrangement. The other two mutually trans Cu atoms are coordinated by two (μ 3-S) atoms, one nitrogen atom of pz Me2 and one terminal Cl or Br ligand, giving a distorted tetrahedral CuS 2NX unit. In addition to being structurally studied by X-ray diffraction, the title compounds have been characterized by IR, UV–Vis and 1H NMR spectroscopy. The IR results, which include low-frequency M–S b stretching bands, are consistent with the X-ray structural analysis and confirm that the [MS 4] 2− cores are coordinated through all four sulfur atoms in the complexes 1 and 2.

Chloride ligation in inorganic manganese model compounds relevant to photosystem II studied using X-ray absorption spectroscopy.

Chloride ions are essential for proper function of the photosynthetic oxygen-evolving complex (OEC) of Photosystem II (PS II). Although proposed to be directly ligated to the Mn cluster of the OEC, the specific structural and mechanistic roles of chloride remain unresolved. This study utilizes X-ray absorption spectroscopy (XAS) to characterize the Mn-Cl interaction in inorganic compounds that contain structural motifs similar to those proposed for the OEC. Three sets of model compounds are examined; they possess core structures Mn(IV)(3)O(4)X (X=Cl, F, or OH) that contain a di-micro-oxo and two mono-micro-oxo bridges or Mn(IV)(2)O(2)X (X=Cl, F, OH, OAc) that contain a di-micro-oxo bridge. Each set of compounds is examined for changes in the XAS spectra that are attributable to the replacement of a terminal OH or F ligand, or bridging OAc ligand, by a terminal Cl ligand. The X-ray absorption near edge structure (XANES) shows changes in the spectra on replacement of OH, OAc, or F by Cl ligands that are indicative of the overall charge of the metal atom and are consistent with the electronegativity of the ligand atom. Fourier transforms (FTs) of the extended X-ray absorption fine structure (EXAFS) spectra reveal a feature that is present only in compounds where chloride is directly ligated to Mn. These FT features were simulated using various calculated Mn-X interactions (X=O, N, Cl, F), and the best fits were found when a Mn-Cl interaction at a 2.2-2.3 A bond distance was included. There are very few high-valent Mn halide complexes that have been synthesized, and it is important to make such a comparative study of the XANES and EXAFS spectra because they have the potential for providing information about the possible presence or absence of halide ligation to the Mn cluster in PS II.

Magnetic Exchange Interactions in Oxo-Bridged Diiron(III) Systems: Density Functional Calculations Coupling the Broken Symmetry Approach

The calculations on magnetic exchange interaction of Cl3FeOFeCl32- and the related modeling compounds were performed by using the density functional theory coupling the broken symmetry approach. The calculated results show the absence of a direct Cl3Fe---FeCl3 magnetic coupling and the effect of the terminal Cl ligands on magnetic exchange interaction in [Fe−O−Fe]4+, while the protonation of μ-oxo bridge reduces significantly the magnetic coupling constant J value. On the other hand, the J value is insensitive to variation of the Fe−O−Fe angle; however, the dependence of the J value on the Fe−O distance can be expressed as an exponential function, while the J value keeps a constant to the variation of the O−H distance in the μ-hydroxo and μ-aqua bridges. Molecular orbital interaction is applied to explain the magnetic exchange interaction in μ-oxo bridged iron(III) dimers. The validity of qualitative magneto−structural correlation for the models used is further confirmed by full geometry optimization.

Comparison of the Manganese Cluster in Oxygen-Evolving Photosystem II with Distorted Cubane Manganese Compounds through X-ray Absorption Spectroscopy.

X-ray absorption spectroscopy has been employed to assess the degree of similarity between the oxygen-evolving complex (OEC) in photosystem II (PS II) and a family of synthetic manganese complexes containing the distorted cubane [Mn(4)O(3)X] core (X = benzoate, acetate, methoxide, hydroxide, azide, fluoride, chloride, or bromide). These [Mn(4)(&mgr;(3)-O)(3)(&mgr;(3)-X)] cubanes possess C(3)(v)() symmetry except for the X = benzoate species, which is slightly more distorted with only C(s)() symmetry. In addition, Mn(4)O(3)Cl complexes containing three or six terminal Cl ligands at three of the Mn were included in this study. The Mn K-edge X-ray absorption near edge structure (XANES) from the oxygen-ligated complexes begin to resemble general features of the PS II (S(1) state) spectrum, although the second derivatives are distinct from those in PS II. The extended X-ray absorption fine structure (EXAFS) of these Mn compounds also displays superficial resemblance to that of PS II, but major differences emerge on closer examination of the phases and amplitudes. The most obvious distinction is the smaller magnitude of the Fourier transform (FT) of the PS II EXAFS compared to the FTs from the distorted cubanes. Curve fitting of the Mn EXAFS spectra verifies the known core structures of the Mn cubanes, and shows that the number of the crucial 2.7 and 3.3 Å Mn-Mn distances differs from that observed in the OEC. The EXAFS method detects small changes in the core structures as X is varied in this series, and serves to exclude the distorted cubane of C(3)(v)() symmetry as a topological model for the Mn catalytic cluster of the OEC. Instead, the method shows that even more distortion of the cubane framework, altering the ratio of the Mn-Mn distances, is required to resemble the Mn cluster in PS II.

Rhodium complexes with secondary phosphine and phosphinite ligands and the crystal structures of [(PPh 2OH) 2(PPh 2O)Rh( μ-Cl) 3Rh(PPh 2OH)(PPh 2O) 2] and [(PPh 2OH)(PPh 2O)Cl(NCMe)Rh( μ-Cl) 2Rh(PPh 2OH)(PPh 2O)Cl(NCMe)] · 2thf

RhCl 3·3H 2O reacts with ca six molar equivalents of PPh 2H or PCy 2 in EtOH solution under a N 2 atmosphere and in the presence of excess NH 4PF 6 to yield [RhCl 2(PPh 2H) 4]Pf 6 or [RhCl 2(PCy 2H) 4]PF 6 respectivley as yellow solids. 31P{ 1H} NMR spectroscopy shows the presence of the trans isomer only in chloro-carbon solutions, with J RhP ca 80 Hz. Upon standing a solution of trans-[RhCl 2(PPh 2H) 4]PF 6 in a MeCH/thf mixture results in the production of yellow crystals of [(PPh 2OH)(PPh 2OCl(NCMeRh( μ-Cl) 2Rh( rmPPh 2OH)(PPH 2O)Cl(NCMe)]·2 thf, the structure of which shows an edge-bridge bioctahedral arrangement with d( Rd… Rh) = 3.74 A ̊ . The NCMe ligands to the terminal Cl ligands, while the PPh 2O and PPh 2O − ligands are trans to the bridging Cl ligands. The crystal structure of the triply-bridged dimer [(PPh 2OH) 2(PPh 2O)Rh( μ-Cl) 3Rh(PPh 2OH)(PPh 2O) 2] has aslo been determined, showing a face-sharing bioc-tahedral arrangement, with d( Rh… Rh) = 3.39 A ̊ . Both dinuclear species show significant POH…OP hydrogen-bonding interactions.

Chlorine K-Edge X-ray Absorption Spectroscopy as a Probe of Chlorine−Manganese Bonding: Model Systems with Relevance to the Oxygen Evolving Complex in Photosystem II

For a series of Mn−Cl coordination complexes the chlorine K-edge X-ray absorption spectra (XAS) have been measured to probe chloride−manganese bonding. Results show that in a series of mononuclear (single Mn) compounds with Cl covalently bound to Mn, the intensity of the pre-edge feature increases in the order MnII < MnIII < MnIV. For a series of distorted cubane complexes (containing 4 Mn) with bridging and terminal Cl ligands, three pre-edge features are seen. The pre-edge peak at lowest energy increases in intensity as more terminal Cl are included in the compounds. The origin of these features in the edge spectra is described in terms of the symmetry and ligand field splittings expected for the Mn complexes. The Mn model systems studied here have potential application to the oxygen evolving complex (OEC) in Photosystem II (PSII), where direct structural evidence for a halide binding site on the Mn cluster in one or more S-states of the Kok cycle would be informative.

Synthesis, NMR Study, and Reactivity of Isomeric Early-Late Heterobimetallic Dihydrides. X-ray Crystal Structure of (PPh(3))HRu(&mgr;-H)(&mgr;-PMe(2)C(5)Me(4))(2)(&mgr;-Cl)ZrCl.

The new isomeric ruthenium/zirconium dihydrides of the formula (PPh(3))HRuH(&mgr;-PMe(2)Cp)(2)ClZrCl (1, 2) (Cp = C(5)Me(4)) have been characterized by elemental analysis and NMR ((1)H, (31)P and (1)H relaxation data). Complex 1, stabilized by Cl and H bridges, has been isolated from the room temperature reaction between RuH(2)(H(2))(PPh(3))(3) and (PMe(2)Cp)(2)ZrCl(2). The X-ray crystallographic study of 1 revealed a bimetallic complex. The six-coordinate Ru atom and the five-coordinate Zr atom are held together by two bifunctional phosphinocyclopentadienyl ligands and by H and Cl bridges. Crystal data for 1: monoclinic space group P2(1)/c, a = 13.901(2) Å, b = 18.205(6) Å, c = 16.633(3) Å, beta = 92.43(1) degrees, V = 4206 Å(3), Z = 4, d(calc) = 1.472 g cm(-)(3), R(F) = 0.056, R(w)(F) = 0.058. Complex 2 with two H bridges and terminal Cl ligands at Ru and Zr has been obtained by an irreversible isomerization of 1 in the presence of HNEt(3)BPh(4). This transformation has been proposed to occur through slow protonation of one of the phosphorus ligands with the five-coordinate Ru center formed by undergoing rapid pseudorotation. Complexes 1 and 2 do not react with H(2), N(2), or 3,3-dimethyl-but-1-ene. Treatment of 1 with 1 equiv of NaHBEt(3) in C(6)D(6) gives a mixture of new trihydrides (PPh(3))HRu(&mgr;-Cl)(&mgr;-H)(&mgr;-PMe(2)Cp)(2)ZrH (3) and (PPh(3))HRu(&mgr;-H)(2)(&mgr;-PMe(2)Cp)(2)ZrCl (4). Complex 3 transforms to 4 upon standing in solution for a period of several days. Under the same conditions, complex 2 leads smoothly to trihydride 4. Both trihydrides are new and have been characterized by (1)H, (31)P NMR, and (1)H NMR relaxation data. Complexes 1 and 4 are fluxional in solution at room temperature, showing hydride exchange between the terminal and bridging positions. The variable-temperature (1)H NMR spectra allowed determinations of the DeltaG() values of 16.4 (313 K, THF-d(8)) and 13.5 kcal/mol (295 K, toluene-d(8)) for the exchange in complexes 1 and 4, respectively. Possible exchange mechanisms have been discussed. Complex 2 is rigid on the NMR time scale.

Die Synthese und Struktur von Clusteraziden: A4[Nb6Cl12(N3)6](H2O)2 mit A=Rb. Cs / Synthesis and Structure of the Cluster Azides: A4Nb6Cl12(N3)6](H2O)2 with A=Rb, Cs

Abstract The new compounds A4[Nb6Cl12(N3)6](H2O)2 (A = Rb, Cs) were synthesized from In4[Nb6Cl12Cl6] by substituting six terminal Cl ligands and the In+ ions in methanolic solution. An X-ray structure refinement was performed on single-crystal data of Rb4[Nb6Cl12(N3)6](H2O)2 (1) (space group P1̄, Z = 1, a = 912.5(1) pm, b = 937.2(1) pm, c = 1062.0(1) pm, α = 96.88(2)°, β = 101.89(1)°, γ = 101.44(2)°) and Cs4[Nb6Cl12(N3)6](H2O)2 (2) (space group PI, Z = 1, a = 920.9(5) pm, b = 947.9(7) pm, c = 1091.8(7) pm, α = 96.89(6)°, β = 103.35(5)°, γ = 101.60(5)°. Each of the centrosymmetric [Nb6Cl12(N3)6]4- ions of the isotypic compounds contains six terminal azide groups at the corners of the octahedral niobium cluster (d̄Nb-N = 226(1) pm (1), 225(1) pm (2), bond angles Nb-N-N 120-127°). The [Nb6Cl12(N3)6]4- ions are linked via Rb-N and Rb-Cl interactions of the Rb+ ions to form a three-dimensional structure. Crystals of the compounds react explosively on heating or mechanical pressure.

Synthesis, Structure, and Magnetic Property of Linear Chloro-Bridged Nickel(II) Tetramer with Dinucleating Bis-dimethylcyclam Ligand

Abstract A new nickel(II) complex with the composition of Ni2Cl2(L)(ClO4)2·1.5H2O (L = α,α′-bis(5R(S),7S(R)5,7-dimethyl-1,4,8,11-tetraazacyclotetradecan-6-yl)-o-xylene) has been prepared via a four coordinate complex [Ni2(L)] (ClO4)4·3H2O from [Ni2(μ-Br)Br2(L)]Br·H2O. The compound crystallizes in orthorhombic space group Ccm21 with cell parameters at −80 °C, a = 21.90(1), b = 20.28(1), c = 19.63(1) Å, V = 8718(1) Å3, Z = 8. The crystal consists of the cationic dinuclear unit [Ni2(μ-Cl)Cl2(L)]+, the counter anion ClO4−, and water of crystallization. In [Ni2(μ-Cl)Cl2(L)]+, three chloride ions and two nickel ions are alternately arranged in an almost linear manner, and two cyclam rings with the most stable trans-III type conformation are arranged in a face-to-face manner. This cationic dinuclear unit is further connected to each other by sharing the terminal Cl ligand to form pseudo one-dimensional chain structure of the ···Cl–Ni–Cl–Ni–Cl··· type. However, one of the Cl atoms which bridges the dinuclear units is statistically disordered at two positions along the chain and thereby the repeating unit in the chain is a chloro bridged dimer of the dinucleating ligand complex. The neighboring Ni–Cl distances range from 2.568(4) to 2.855(4) Å. The temperature dependent magnetic behavior in the range of 25—300 K has been interpreted by the usual Heisenberg–Dirac–Van Vleck model, assuming that only three Ni(II) ions in {Ni2Cl2(L)}2 are paramagnetic. The best fit parameters were J = −48.2(3) and J′ = −11.2(3) cm−1 for = −2J(S1·S1′) − 2J′(S1·S2).